Hi and

As
Dungahass said, we understand what you describe. I could relate to a lot of what you wrote about staying quiet and not saying anything in an effort to not escalate or cause any problems. I am here primarily due to my mother's mental illness, but I believe my ex had BPD traits at the very least so yeah, I get it.
He can get help, but will he? And if he doesn't, is this my life?
We have had many members who have improved this for themselves by learning new relationship skills that can make life easier for you, help you cope better and give you a better chance of being seen and heard in the relationship, so no, this is not necessarily your life. Things can get better. None of the tools and strategies we use here, including validation are intuitive and they take some practice to get the hang of.
What can help is to learn about the disorder and what is going on when he behaves the ways he does. Knowledge helps us depersonalize the behaviors so we can respond in healthier ways. Staying quite and agreeing is not the best way to go about things, though i am a fan of picking your battles and knowing when to stay quite. The thing is, you need a place and a voice in your relationship. At the same time, these relationships are difficult and require that we, as the healthier ones, carry the lions share of problem solving and being emotionally healthy. It can be done.
am I just supposed to 'feel' like deep down that he loves me and this is just BPD? Because that may last for a little, but over the years, it's wearing me down. I'm not sure how to feel.
Chances are when he says he loves you he means it. Unfortunately, when he says he hates you, he means that as well. For pwBPD (people with BPD), feelings = facts. this applies in a lot of their thinking and what they say and do. BPD is a disorder of emotional regulation so emotions rule. It is also a disorder that affects their most intimate relationships and a lot of the time their behaviors do not manifest with friends, co-workers or other family members they are not close with. BPD behaviors seem to be triggered when they are at their most vulnerable.
Anyway, I don't want to give too much info all at one. We do have a lot of reading material here and I hope you check out some of the articles tacked to the top of the board. I also hope you feel free to jump into other threads, ask questions, etc. We all support and help each other here.
Again, I am glad you are here.