Hi Flapjack,
I know how it can be to have associations that cause you to have flashbacks. I would suggest talking to him and explaining to him how you are feeling. A good friend will understand, and you can take it from there.

I am a bit concerned though that this guy is making sexual remarks to you, and that's where boundaries come in. I would tell him that you are uncomfortable with his remarks and if he persists, then he may be someone you'd be better off not associating with.I understand you have a friendship with this person and you feel the need to be there for him, but if it is causing you emotional distress I would not put myself through that if I were you. If he is going through a rough time and is at times suicidal, well it is not your responsibility to handle his problems. There are others he should be reaching out to, such as a therapist or other health professionals that are equipped to handle things such as he is going through. Right now you just have to focus on you and doing what is best for you. You are a good friend to want to be there for him, but believe me he will find the help he needs. Just don't sacrifice your own well being for someone else, especially in this case. Whatever you decide to do, I trust your judgement and I'm sure you'll do the right thing for yourself in the long run.

Take Care!
Love,
Sujin