Instead of spending Saturday nights out with the girls, you're suddenly staying in with your new guy staring into each other's eyes over romantic dinners. When your BFF gets snippy, acting like your date nights are dumb or your beau is somehow bad for you, you may start to wonder if she's being sincere or jealous.

Crude Comments

"Man, your girl's just not hot." If this is the norm when it comes to your bud commenting on your girlfriend, consider the possibility that he's jealous. While crude, rude or disparaging statements may seem mean-hearted, it's possible that they're coming from a place of envy and not hatred. A new romantic relationship may seem threatening to an existing friendship, according to clinical psychologist Gerry Heisler in his "Psychology Today" article "Are Your Friends Trying to Ruin Your Love Life?" Acting out by verbally cutting down your new partner is a sign that your friend is feeling pangs of jealousy in the face of your new romance.

Uneasy Actions

A jealous friend may take the idea of making rude statements a step further and actually act not-so-nice to your partner's face. While being mean or snarky behind his back is difficult enough to deal with, when your best friend offends your boyfriend directly, this can quickly cause problems in both relationships. If you feel an uneasy tension between your girlfriends and boyfriend, it's possible that jealousy is at the heart of the matter. For example, you and your BFF always go ice skating on Sundays. Suddenly you are inviting your guy to tag along. The jealous feelings that your friend has can come out as mean comments to him or icing him out of conversations.

Possessive Behaviors

Think back to your younger years and how you quickly snagged your favorite toy away from another child who was ready to grab it. In your friend-girlfriend relationship, you're the toy. While it's likely that both people involved understand that you're an actual person -- and not a toy -- acting possessive is a red flag for jealousy. Demanding that you hang out with him and not your girl or pushing her out of the picture by not inviting her to parties or on group outings shows that your friend is acting in a possessively jealous way.

Self-Esteem Issues

Low-self esteem is a possible reason for relationship-oriented jealousy, according to psychologist Suzanne B. Phillips in the article "Is Jealousy Threatening Your Relationship? Five Checkpoints" for "Psych Central." If your best friend tells you she's scared that you'll replace her with your guy or that she feels like you would rather be with him, it's likely that she's jealous. Keep in mind that she doesn't always have to say outright that she has low self-esteem. She might seem sad when you bring up spending time with your guy or even back away from you, feeling like she's not wanted.