Do people believe that the first serious relationship could lead to marriage/lifetime togetherness?

Its both our first serious relationship and i do think that this could be it he's perfect in every way but then i also feel like what if he doesn't feel the same? Like he's completely inexperienced when it comes to relationships do you think guys think that they should have 2 or 3 before settling down or do they settle down when the girl is right even if the first one

Ive always heard never select the first one I love him i do but i feel like im wrong holding him down