Am I the only one that thinks Ash might be pretending to not get romance on purpose? Possibly either to avoid the drama, avoid having to hold a girl back from her own dreams, so that he can focus on his own dream, or a combination of all three reasons. I think this because sometimes Ash acts clueless, yet, there are other times when it seems like he does get it. Further, it seems like the longer the Anime goes on, the more clueless Ash acts, which could mean he is getting more used to performing his act. I also noticed that, character development wise, it would make sense for Ash to make this decision. When Misty left, she became a Gym leader, while mostly all she did when traveling with Ash was was help him achieve his dream. And shortly before May left, if I remember correctly, somebody commented on how May kept watching him battle and ended up battling a lot like him, therefore somewhat hindering her in contest battles, the look on Ash's face when he heard this was pretty emotional if I recall. Clearly both of these events, in combination with why Ash let Charizard train in Charicific vally, and why Brock left, and others, would instil a mindset that it would hurt others if they stayed with him. And then we still don't know how Ash's own father fits into this equation.
Plus, Ash would not even settle down to be a frontier brain, settling down to raise a family is almost out of the question at least for a very long while.
So, the most interesting thing about Serina is that she does not have a personal goal in the Anime yet. Based on my theory, if Ash does fall in love, the person would either have to have the same goal as him (collecting badges etc) or otherwise have a goal that lets them travel together with little to no hindrance on either side. If the girl has no goal other than being with him then, how Ash would feel about that is kind of up in the air. Ash might be waiting until Serina decides what to do with her life before he gets his hopes up, which could make things complicated if the writers actually want to confirm this theory,
Oh, and kids do get romance, mostly because of Disney lol. It's just a sexual relationship that would be out of the question due to the target audience and love does not require sex you know, especially if you're only 10-12 or 15 years old or however hell old Ash is now.