On this Dating to Marry discourse, I remember Michelle Obama talking about how Barrack never wanted to marry her because he didn't believe in marriage due to how his parents' marriage crisis. Michelle desperately wanted marriage because she comes from a stable family.

Barrack was reluctant which frustrated her and she practically had to beg and pressure him to marry because she wanted to spend her life with him but as a wife. Barrack wanted her in his life but didn't see the need for legal commitment.

He finally conceded to make her happy.

I guess several factors influence people's marital decison and just because they haven't proposed doesn't make them serious. This is why youndiscourse with your partner to understand where they are coming from.
Michelle knew why he wouldn't propose and so she could make her case.

Stop the silence and assumption. As the relationship grow, open your mouth and have discussions so you don't claim anyone is leading you on or accuse them of being unserious.

Learn to open your mouth and express your earnest desire. Your opinion matters as much as theirs.

It may or may not lead to marriage for varied reasons and sometimes, that is okay. This is why you should discuss and understand why.

Good luck out there.