How would you deal with an awkward situation involving a friend and a significant other?

How would you approach the situation?

You’re having your 4-month anniversary with your girlfriend. Your acquaintance-friend, whom you see on weekends sometimes for group movie nights, invited you both to a Halloween party, but you forgot to respond, you happily spent the time with your girlfriend. Previously, though not necessarily recently, the acquaintance-friend, who considers you to be a close friend because he has few, has hit on your girlfriend for some reason—perhaps because he did so before you two started dating. Even if you jokingly ask him not to, he has done it multiple times. On the anniversary/night of party, he texts you asking, “So, are we still friends?” and you respond in a nice way, all-be-it by text, “We’re definitely still friends, though to be honest I haven’t felt entirely comfortable hanging out outside of movie night because he has hurt your feelings by hitting on your girlfriend, on top of that it was the 4-month anniversary and my girlfriend and I didn’t have costumes, although I admit should have responded earlier and I’m at fault for that.” after some wine at 3am.

Note: It’s a girl-girl romantic relationship, thus the guy might not take it as seriously as a male-female relationship.

How would you deal with the awkwardness? He probably wasn’t expecting that answer and he hasn’t hit on my girlfriend in a while. All I could think of was to be honest, but I am inept at dealing with awkward situations. I don’t like that I said that in a text, but I felt like I was going to explode if I didn’t tell him that it hurt my feelings when he hits on my girlfriend (Going on for months off and on, usually because of alcohol. He’ll hit on me sometimes too, but he knows my girlfriend better. I’m not a jealous, possessive partner, it’s just a pet peeve of mine when someone disrespects me by hitting on my girlfriend in front of me and doing it again… and again. He probably thinks it’s just fun teasing, but it’s been hurting my feelings.), and I guess it wasn’t his fault he didn’t realize it was our 4-month anniversary the night of the party. So now how do I deal with an awkward situation with a possibly socially awkward person?

Usually I just ride awkward situations out. Maybe I’m just not used to standing up for myself or what I think is correct.