Here are the guidelines:
Men date women hoping for sex. A few, who are ready to marry and have their career and finances in order, also look for a partner. But even they are motivated mostly by wanting sex.
A guy is interested in you IF he asks you out. If he doesn't chase you, then either he is not relationship-ready, or he just is not that into you. And he doesn't care if someone else steals your heart.
IF he has been steadily dating you for at least 6 months, it is safe to say he likes you ... OR he likes the sex.
If he has been dating you at least 1-2 years, and THEN asks you to marry him, then he probably loves you. Asking you to move in may not indicate love. It may just indicate convenience for him until.