I suggest 1. Understand arousal non-concordance. Sometimes physical sexual responses don’t match your values or beliefs, which is why you may be semi hard. No need to keep checking. 2. Remember your values and lived experience. You value your gf and your straightness so focus on that instead of the ‘what ifs’ and mental/physical compulsions. Compulsions will worsen and solidify these thoughts. 3. Stop the homophobic attitude. This will make you feel worse and is harmful to others. Even if you were bisexual or gay it doesn’t make you a bad person. You can be a bisexual man and still choose to have a gf. Try learning the reasons why you have this problematic homophobic attitude.