Whatever the case, you don’t deserve to be treated as such and you have every right to call someone out if they are treating you that way.

While being on the rebound is not necessarily cheating, it is just selfish and inconsiderate to keep someone around to fill a void. Healing from a break-up is a journey that should only be undertaken alone, not with a new partner.

How can you love someone else if you don’t even love yourself?

If you do find yourself in that unfortunate situation where you simply feel that you are not enough, what should you do? And what are the telltale signs to look out for?

Should you talk about your exes with your partner?

Valentina Tudose, relationship expert and certified hypnotherapist, says: “In love, we all want to be number one, and to feel chosen and special to someone. But, sometimes, we end up being second best and that never feels good.

“Some people start a new relationship before they completely let go of the past and they are still attached to a previous partner. For the new partner, it can be difficult to deal with the ghost of a past relationship looming over the current one.

“This tends to present itself as emotional distance, or arguments stemming from past hurts rather than issues relevant to the current relationship.”

This isn’t always the case, and some people are perfectly content in a new relationship. But sometimes the same can’t be said for their ex, who may be hell-bent on tarnishing your new-found happiness.

“When your partner’s mood and emotional balance depend so much on a third party, it’s hard not to feel like you’re just a substitute,” Tudose says.

“If you feel like your needs are not being met, you need to take action and communicate your feelings openly.”

On how to change your situation from being a “replacement” to becoming “irreplaceable”, Tudose offers the following advice.

“It’s often easier for some people to detach from an ex when they found new love, but it’s not always easy to deal with that healing process when you are the new partner.”

First, she advises focusing on the reasons your relationship is the right one for both of you. Ask yourself how you are contributing to each other’s lives and consider your compatibility.

“Ensure you have a common vision and that you share the same values. Making clear and conscious agreements as to how to have your needs met will set you apart from the ex. It will make your partner understand you are the upgrade and it’s time that they let go of what didn’t work in the past.”

Tudose says if you help your partner learn their lessons by showing them what mature love feels like, they will be more open to letting go of the past. But you must also look out for the signs that you may in fact be fighting a losing battle.

“Sometimes, it’s just not meant to be. If you feel you are being used and ‘breadcrumbed’, which means you are living off scraps of attention and affection, it’s time to consider how this relationship is harming you more than helping you.

“Spend some time identifying the behaviours you are not willing to tolerate. Give your partner a chance to adjust them by making clear requests of what would need to happen for you to feel happy and loved in this relationship.”

After you have done all that, set clear deadlines for when changes need to happen.

“If it works, your partner is both listening and healing from their pain so your relationship is heading in a good direction. But be ready to walk away if nothing changes because things will only get worse,” she says.

Knowing when to bow out is very important because we all deserve a relationship in which we are not constantly doubtful of our partner’s feelings for us or whether we are measuring up to someone else.

At the end of the day, we are all deserving of love – but it should never come at the cost of someone else’s happiness.

Luisa Tam is a Post correspondent who also hosts video tutorials on Cantonese language that are now part of Cathay Pacific’s in-flight entertainment programme