When two people in a marriage are living by significantly different codes of observance, this has the makings of frustration and conflict. Regardless of how much you like the person you are dating, if you are both planning to maintain meaningfully different levels of frumkeit, you are setting yourselves up for serious issues down the line.
However, it matters greatly the “what” and the “who.”

What – There is a huge difference between major religious differences and minor ones. While “major” and “minor” are relative terms, it is still often possible for someone to thoughtfully consider whether the specific issue of difference is something that should rightfully be considered “major.” An issue may also be judged as major or minor depending on the extent to which it affects the other party.

It is important to remember that any normal marriage will involve compromise. A degree of give-and-take in a marriage is completely normal and necessary. So, being able to come to agreement on smaller issues is a pretty important skill to develop for marriage.

Who – People vary in how flexible they are. Some people are ready and willing to adjust their ideas and behavior, while others find that prospect mildly traumatic.

So, know yourself. If you are the kind of person who is comfortable accepting change, you should be able to agree about minor issues.

On the other hand, if you struggle to compromise and cannot find a way to bridge the gap you need to think very carefully whether this is going to work, even if you feel very warmly towards your date.