Normally i'd say that ISTPs can really live in a moment by moment basis, so they can feel intense love for a person one day and total indifference another day. But that's in general, and pretty early on in relationships. Once in a relationship, they aren't so wishy-washy, and if they are there, then they are there and they're not going to leave unless something drastic happens.
But yeah, I don't get this guy. Reading through the comments here, I kinda agree with the majority also... You don't treat someone you love this way. He sounds like he has issues and he needs to work them out before he can even be in a relationship. And for goodness sake, he needs to be reliable/consistent.
This isn't type specific; If someone likes someone enough, then there will always be a way. I don't know what to suggest. It's up to you if you want to give him a chance to explain himself. We have no idea what his intentions are and what he really feels for you, and what trying to contact you after 3 months of no contact to tell you he loves you (after so long without contact??? really? That doesn't look very promising), and then trying to contact you a few times in the last 3 months means.