Puzzle answered this really well. I also wanted to add my own experience.
I am Catholic ( converted when I was 19 and like you, considered myself a Christian but was never baptised as my parents didn’t chose this for me as an infant ). I wanted to be baptised in the one true faith.
Anyways, my husband is not baptised and he comes with me to mass and believes most of what the church says except some issues, which perhaps he hasn’t fully explored.
When we went to speak with a priest about marriage, the priest said one can be spiritual and not necessarily religious and that this too was important. Basically he said that no conversion was required, and the church does have a somewhat lengthly process to convert. (not painful though!! very englightening and wonderful). The priest said maybe one day my husband would convert ( and maybe not ).
The married technically has to be allowed by the local bishop due to “disparity of cult” is what I think it is called. This process is so common that I doubt the Bishop actually looks at each case individually and an interview with the couple by the presiding priest is likely sufficient in most dioceses.
The only thing our marriage isn’t, is “sacramental” because my husband is not baptised. Should he ever be baptised, in any Christian faith, it will immediately become so.
Be honest with your wife about how you feel about your spirituality, and the church and Christ. Do you two pray together? Just because you aren’t Catholic, doesn’t mean you can’t do spiritual things together.
Don’t of course lead her on that you may convert one day. You may one day be moved by the Holy Spirit to convert but there should be no pressure on you.
A lot of people on this board, and elsewhere in the Catholic community do warn against mixed faith marriage. It isn’t easy.
One of the common stumbling blocks is NFP… whether to use articificial birth control or not. (ABC). You have to discuss all the tricky issues with each before marriage to ensure an understanding of what your life is going to be like after marriage.
Congrats on the engagement and all the best to you!