I'm worried about the validity of marriage if he doesn't obey the rules (because I can't control his actions).
Now that you clarified what you mean by "doesn't obey the rules", I can be more direct and specific.
You said the issue was birth control.
That is actually one of the things a proper Catholic marriage preparation will screen for.
A priest would sin if he consented to witness to an invalid marriage (which would be "annulment bait", and basically allowing a couple to pretend they are married, but they would actually be fornicating), just like a bishop would commit sin by knowingly ordaining a bad candidate for the priesthood.
To fulfill his duties in this matter, the priest has to look for all the things that might invalidate the marriage:Do you intend for marriage to be exclusive?
Do you intend to have the children God sends you? Do you know that birth control is a mortal sin?Do you know that marriage is for life?
Is anyone forcing you to get married? (a related question is, "Are you pregnant?")
Are you both of sound mind and (reasonably) good health? Is either one of you sterile?
Are either one of you misrepresenting yourself to the other (saying you're heir to a great fortune, for example, if you're actually unemployed; or claiming to be a person you're not.)
Those are things that can invalidate a marriage.
Because certain things affect the very nature of the marriage contract.
Marriage is a voluntary, two-party contract for life, in which a man and a woman give each other exclusive rights over their bodies, promising to live in common and beget children (however many God sends) and raise them Catholic.That's why you can't have coercion, lack of the use of reason, or a false notion of marriage (birth control, possibility of divorce later).
But interestingly, other things do not necessarily affect the marriage contract -- at least the priest during marriage prep won't ask about them:
Problems with anger
grudges
addictions, past drug use
employment record
prayer life
criminal record
past murders
etc.
These things are important for YOU to know about, but they don't affect the validity of a marriage. Intent to use birth control is actually able to invalidate the marriage from day one.
I agree with others who said that loving people is one thing, marrying is another. If you feel called to a special life of prayer and sacrifice, perhaps you should look into becoming a religious sister.
As I tell young men about the priesthood, the same applies to female religious: namely, that religious sisters aren't a bunch of "asɛҳuąƖs" or "lesbians" somehow defective in normal female feelings or hormones. They are normal females, giving, loving, but they have chosen to give themselves to God in His service, and love countless people by teaching, praying, and sacrificing for them.
I will go so far as to say this: if the man you describe is the best man God ever sends you, then He obviously doesn't intend for you to be married. But that is a "worst case scenario"; there is no need to give up yet. It is more likely that God will send someone better in response to your fidelity.
I know this is VERY hard to take; I've been there before myself. The women on here can handle this better than I can (a fellow woman is better to talk to, for this sort of issue). But being faithful to God is paramount, and you will be surprised how God will take care of you when you place Him first.
Apparently a lot of the horror stories people have posted on CathInfo about bad marriages took place in the past, posted by members who are no longer here. We've had LOTS of stories in the past from hapless men and women who are now stuck in bad marriages. I would be careful.
I would especially beware letting pity enter in to your decision about marriage. I actually knew a young man who came very close to marrying a very messed up woman. Fortunately for him, it didn't work out. The man actually told his family members who objected, "I can't just cast her off; if I don't marry her, then who will?" and things like, "You want me to judge her?" Seriously, he said that! Just from what I knew of the woman, I'm sure he would have been miserable, but in the worst kind of way: the way that costs you your faith and/or your soul.
I second what Songbird said:
Love, be charitable, have mercy all you want -- but only marry a good solid Catholic!