Can you tell me how i could be more assertive with my boyfriend?

Whole relationship: This will take practice, and knowing that a man worth keeping is a man who will listen to your reasonable requests. A couple never agrees on everything, and you should try to do what you can do accommodate each others' wishes for the sake of the relationship. If he's worth having, you'll discover that he'll be grateful to know what you want -- it annoys a man if you don't communicate.

How to practice: Dr. F gave great advice. I'll add that like he said practice/role playing is key. You can work with a therapist to practice assertiveness either individually or through couples work. You can also start by practicing with a trusted friend/relative who has these skills. Learning a new skill takes repetition and a bit of risk. Know that it probably won't feel comfortable, natural at first.