I (late 20’s/F) found out a friend (early 40’s/M) has secret intentions to sleep with me and I don’t know how to proceed with this friendship

I’ve known this friend (We’ll call him K) for nearly 6 years now, and we’ve never met in person. We have a mutual friend who I’ve known for even longer (I’ll call him M) and I have not met him in person either. M Knows K and has known him for nearly two decades. I met K through M and over the years I became pretty good friends with K. This past year or so I feel that our friendship has really blossomed to a new level, to the point where I’m quite comfortable sharing intimate details about my personal life with him. We talk daily, share lots of memes, game together, and sometimes call to talk about more serious stuff.

A little while back I was interested in the idea of meeting up with him to go to a concert together, which would have meant him having to make a roadtrip to where I live, picking me up, and taking us to the city where the show was. This meant getting a hotel for the night, which he kindly offered to pay for, while I would supply the tickets. Some stuff came up that prevented him from being able to go so we had to cancel those plans and hope for another opportunity down the line. But during this period of planning, I spoke to our mutual friend M about it and he seemed like he didn’t have any concerns and thought it sounded fun for us, but then he added in a joking manner “ K’s going to try to sleep with you “ and I had a laugh and didn’t think much about it beyond that at the time.

Now, my favorite band is touring again and he’s offering to pay for me to fly up to the city that’s closest to him (still several hours from his home) as well as cover the cost of pit tickets and a nice hotel. This could easily total somewhere over a grand, all on him, his treat. The offer is awfully tempting and needless to say extremely generous. It’s a bucket list fantasy of mine to see this band and rock out in the pit with a good friend. But it seemed a little too good to be true, and I couldn’t help but get suspicious about his intentions and start getting some bad feelings about the whole thing.

A little bit of backstory before I continue, I’m in my late 20s, and K is in his early 40s. He’s also married and has children. I realize that age and life experience gap can raise an eyebrow, but despite this we’ve always got on very well as friends with virtually no weirdness towards me to speak of over my entire 6 years of knowing him. I’ve known from our mutual friend M that he can be a bit of a party animal but that deep down inside he is a good person, and I have seen these good qualities myself through the years from him being a genuine friend and being there for me during some very hard times. 

In recent weeks, and before the invitation to the concert, it’s come to my attention that K finds my appearance attractive, which he admitted himself in the form of a compliment when I shared a photo of my new hairstyle. He knows I have self esteem issues and he kept it polite with the initial compliment, but later reiterated over a phone call “ you’re hot! “ in a very friendly tone, which really only made me feel genuinely good about myself. 

So after his invite, his praise over my appearance, and the past joking remark from M, all of this started to piece together in me a feeling of suspicion, and I spoke to M about it and asked him what’s going on, what do you think his intentions are? M revealed a lot about K to me and his attempts at getting with other women (keep in mind this man is married and has children) and how he behaves when his wife isn’t around, which according to M, she doesn’t even know about this side of him. Along with this he alluded to K’s experiences with partying, drug usage, political beliefs, racist humor, the whole nine yards, and from the sound of it this behavior is ongoing. This really painted a picture to me of who he is and M agreed with me based on the evidence I presented that it is extremely likely he has intentions to get me into bed. The kicker about all this too is that I’m a lesbian and M told me that “ that doesn’t matter to him. “

This all came to light a few days ago and I haven’t been able to shake this since. I see K in an entirely different light now and it has me feeling sick to my stomach. It’s left me questioning the authenticity of our entire friendship in hindsight, and right now I feel like I have to wear a mask to keep up appearances with K for fear of causing a rift between him and M, or blowing up our entire friend circle if K’s intentions were to come to light.

I don’t know how to carry on with our friendship after this. I can’t stomach the idea of playing games, chatting and having a laugh with him like we used to. And there’s no way in hell I’m ever going to allow myself to be in a situation where I will meet him in person and be alone with him now. How do I go forward with this relationship? I’m depressed and feel like I just lost a friend, but still wrestling with wanting to be able to maintain that friendship. I just don’t see how I can do that in good faith.

TL;DR; A very good friend of 6 years has highly likely intentions to sleep with me and is using an expensive trip as bait, while a mutual friend has shed light on a darker side to him I was not aware of, which has left me feeling that most of our friendship has been a sham.