When and if Ash ever does get a g/f or settle down, I just hope it's either Misty or May. While I'm hoping for Misty to end up with Ash, the first girl a guy meets usually isn't 'the one'. May could possibly be the right girl for him. As a fan of these characters, I hope they all find love someday with someone at least; Brock, Tracey and Team Rocket as well.
It's possible Ash might never really fall in love but feel a need for a woman in his life and, thus, settle with someone compatible who makes him feel comfortable. He is a young buck now, but he displays many basic male characteristics so it's not outrageous to think he'll have a mate one day, or at least a girlfriend. He might date both Misty and May and then die suddenly before anything deep occurs, who knows? I wouldnt' say Ash is too imature for a relationship currently, just too focused on other things. This isn't the same Ash from season one, he's matured a bit, I mean he's been a mentor to other trainers already.
Of course these are TV characters, so if Ash does become romantic, it'll probably be the predictable fantasy type situation where his first choosen love will be his true permanent love. When I think about most of the couples that formed in Ash's presence during his travels, I believe most of the couples where friends for a good while. I'm thinking of those kids with the nidorans on the Orange Islands
Anyway, to sum it up, nothing is for sure but I hope either Misty or May winds up with Ash. Hopefully he'll give them both a chance.