I had an amazing 11 months with him he was my best friend. It is such a confusing shock to the system to be discarded abruptly though. Psychosomatic symptoms and grief cycle have been intense.
With a normal relationship - ie with a non-BPD partner - it's easier to stay friends afterwards because you're 'out of each other's system' amd don't want to e involved romantically with each other but as you'll know, a BPD relationship is not so easy to make a clean break from because at the time it was the most intense and seemingly perfect relationship we've ever had.
Because your relationship was so good and intense, you'll find it hard to simply close it down and will want to rekindle it - as we all did when it happened to us. For the BPD partner, though they may have feelings for us they also see us as a commodity; a resource to use and fall back on when and if needed. That is the nature of their illness and we have to be aware of this. They can come back to us only to promptly drop us again as their emotions dictate.
Even if they're seeing someone new they will keep us 'in reserve' rather than end up being totally alone and we can never be sure they're keeping contact with us for the right reason.
If you're willing to accept this then by all means try to be friends but try not to read too much into his responses. I'd limit any contact to just the occasional 'Hi, how's things?' and if he doesn't respond then don't press it any further as the ball is in his court. The more you put into it the greater chance of you being hurt again. Just my thoughts.