You should file a police report. The investigator and the District Attorney's Office will decide if they have enough to bring charges against the person. The fact that you were drunk will play a role but the fact that you told him no will play an even bigger one. It seems that you were lucid enough to say no. You should consult with a family law attorney in your area to handle your custody battle. There are some family law attorneys that offer a free consultation, but many charge a nominal fee for their consultation. Good luck.
Legal disclaimer: My answers are only intended as general legal advice based on my experience. They are not intended to be a binding legal opinion nor to create an attorney-client relationship.
From the way you phrased your question, it sounds like this child has already been born, which means the actual sex act occurred some time ago. If this is the case, your options regarding the filing of a police report may not be as effective to keep him out of the baby's life. Any sexual contact without consent is rape, but proving the rape in a court of law can be difficult, especially when time has elapsed. Consult with a local family law attorney as soon as possible.
You say that a guy had sex with you, without your consent, and while you were drunk, and that the incident resulted in your pregnancy, and eventually a child. In Texas, the crime you are describing is aggravated sexual assault, which is committed if a person "causes the penetration of the anus or sexual organ of another person by any means, without that person's consent." It doesn't matter if it was violent or not. It doesn't matter if you were drunk or not. If it was without your consent, it is sexual assault. That is a first degree felony carrying a potential penalty of 5 to 99 years, or life imprisonment, and a fine not to exceed $10,000. Generally, the statute of limitations for this offense is 10 years from the date of the incident, or 10 years from the victim's 18th birthday, whichever is later.
Although a life sentence is one possibility, the offender could also get probation, so there is an extremely wide range of punishment available at sentencing. Judges and juries are allowed to make the punishment fit the crime, including all of the surrounding circumstances.
A conviction is a distinct possibility under the facts you have provided, though I wouldn't think a conviction would be a "slam dunk." The prosecutor will have to establish that you didn't consent to the encounter, and the jury may require some proof other than simply your testimony.
If you were under the age of 17 at the time it happened, lack of consent is easy to establish. If you were 16 years of age or younger, you couldn't consent legally. The male would be guilty unless he could establish both consent and that his age was within 3 years of yours (the so-called "Romeo" or "Romeo and Juliette" defense.)
Contact a lawyer if you want further clarification. Best of luck to you.
This answer is for general purposes only, and is no subsitute for specific legal advice that would come from an attorney hired by you, having full knowledge regarding the facts and circumstances of your individual situation. This correspondence does not create an attorney-client relationship, and you should consult with one or more attorneys prior to acting on any of the information provided in this response.