Quick Answer: First of all, my condolences to you for your loss. I can only imagine that you still miss him and grieve his death. At the same time, his death must also affect your new relationship in profound ways.
My standard answer is to seek professional help, teasing through all the pieces of insecurity that are intensified after a suicide. Likely, you have your insecurities about your ability to love or to be "good enough" that all of us have, but on top of that you have to deal with feelings that if you had just been good enough, or if you had just been loving enough, your boyfriend would have chosen not to take his life.
A good therapist will keep reminding you to consider that this last part is a myth. A suicidal person who does not seek professional intervention will likely make a suicide attempt because of his own sense of hopelessness and despair. He can only borrow the function of another person for so long. You could of -- and very likely are - been absolutely loving and nurturing, and yet he still could have - and did - taken his own life. Therapy can also involve your new boyfriend, and the sessions can help him become a part of working through your feelings without him needing to solve them.
Part of what will help is to evaluate benchmarks: that is, go back in your history with various people (family, friends, and boyfriends) and name the times you have demonstrated love. Recall also how that love was positively received. I bet you can think of times when you know you are a loving human being. Do the same thing towards benchmarks of being good, and how that was received by yourself and others. Benchmarks will help you have a more realistic view of your abilities, so when the feelings come up, you can sort through them with a sense of reality.
Feelings are like ocean waves. They peak and trough, but you notice that they aren't going to swamp you. When you have these feelings, look for validation for what may be really true -- that you are worried about your present relationship and all the thrills and fears that come with it, especially if you are feeling happy with the relationship.
Finally, talk to your boyfriend about these feelings, asking that he just listen and not have to soothe your feelings for you. If he's in the right space to do this, he can reflect your feelings back to you and give you feedback on how he perceives your ability to love and to be good enough.
Good luck.
Quick Question Lady
