Am dating this lady but am very confused.?

We were once the most happiest couples until recently that things have turned sour.She was my FIRST lover but unfortunately,my rival guy by hook or crook was able to win her(We were in different college).Just as things went on without my **girlfriend** telling me everything they did in school,this guy broke my lovers virginity and made her pregnant.During her gestation period they had numerous times which makes me so mad and a dummy(am a virgin guy at 26yrs).My **girl** conceived and lately i saw her.I realised that i still love this girl so much that we came back into a relationship.Now she wants me to marry her,but am just in a big dilemma because i have to take this child of my rival as my own which is causing me woes.She has all her hopes on me marrying her because she claims she loves and loved me more than my rival,and( her childs father).The most annoying aspect is they still talk on phone like lovers and this girl also talk to on phone the same way to.She is putting on **2 faces** and feel embittered in my heart.I love this girl sooooo much and dont love any girl again,but her past is worrying and disturbing me to.Am a virgin and feels like she has really cheated me soo much.She is vowing to curse me if i fail to honor my promise of marrying her.I also feel bitter taking and caring for my rivals child as mine,what should i do?I love my girl so much.Am in such a dilemma because am the jealous type because of how gravely i love her.Someone has taken all the good things in my girl and has left me with nothing.Do u people think she is worth marrying?I always cry about this!!!!