Tatian, a few words if I may:
First, if you have been with her three years and don't clearly feel God's call to marriage with her, how many more might it take to convince you in either direction? (This is just meant to get you thinking, rather than to suggest an answer)
Second, becoming a priest is an amazing response to a supernatural call. This allows a man to become the bridegroom of the Church. Good for you for discerning this possibility, even if you should not find God calling you here.
As for the ex, perhaps the breakup was indeed the best thing. Often, after we make a decision, some of us (me, especially) tend to immediately regret it. Sometimes we almost seem like we always want whatever it is we don't have at that time, but upon receiving it, fear that what we had was better. If this applies to you at all, I recommend taking it to prayer, and spending time in silence with Christ in Eucharistic adoration.
Also keep in mind that although an interfaith marriage can work, we are all primarily called to be saints. That said, in a potential spouse we should look for someone who is going to help us and our children to become saints! This is of prime importance.
Dr. Anthony Buono actually just published a piece on choosing a good woman today:
There are many people with whom we could fall in love and live a happy life. However, there is only one God, one life, and one chance at salvation. That said, always remember that the canonized saints have been human beings, just like us, with similar temptations and choices. Sainthood IS within the realm of possibility for each of us, and is in fact our critical directive!
Strive to grow in Christ, seek him first, and trust that he will lead you closer to him.
Finally, this simple prayer may help:
"Father, I submit to you. Jesus, I trust in you. Spirit, I welcome you. Blessed Mother, lead me to your Son."
Take time to thoughtfully understand and articulate what you mean in this prayer, and rely on the pillars of the Eucharist, Marian devotion, and faithfulness to the Church, and you can't go wrong!
Just my humble two cents,
Addendum: I also have some reading recommendations for you.
Discerning the Will of God, by Fr. Tim Gallagher OMV
Be a Man!, by Fr. Larry Richards
To Save a Thousand Souls: A Guide for Discerning a Vocation to Diocesan Priesthood by Fr. Brett Brannen