To an extent, yes.
A girlfriend asking about your past relationships in the vain of something relevant, is warranted.
For instance, she asks about how long your past relationships have lasted.
That’s a relevant question and asking her the same question in return is warranted too.
Both parties have a right to openness, as long as inquiries are relevant to their relationship.
Refusing to talk about anything concerning your past relationships feels like you are hiding something.
Remember that your girlfriend doesn’t know you all that well.
She didn’t grow up with you nor has she been your friend for eons.
Given this history, she has every right to vet you by asking relevant questions.
There are lines that she mustn’t cross this early, but as long as she doesn’t ask you anything that crosses that line, such as asking for specific personal information about an ex, she is within her right to ask you about past relationships.
Being tight-lipped about this amasses doubt in her mind about the nature of her relationship with you.
When she is asking repeated questions pertaining to a relevant topic that doesn’t cross the line, and you are consistently tight-lipped about it, seeds of doubt are being planted in her mind.
A partner who consistently experiences doubt in a relationship, loses trust in their partner over time.
A loss of trust for a partner is a major factor, as your partner has to trust you, assured that you are honest and true.
Being tight-lipped about relevant questions in relation to your past relationships forces her to create stories in her mind.
Once mental storytelling activates, it is difficult to rein it in.
She creates stories about what your past relationships must have been like.
With your lack of forthrightness, she visualizes abuse or cheating on your part.
These are imaginary stories in her head that she extinguishes moments after they form, but they keep coming back, again and again.
The more circumspect you are to talk about your past relationships in any capacity, the more potent these images are over time.
Ultimately, she forms an entire opinion about you based on those mental stories.
Her conclusion isn’t positive and it affects your relationship.
The evidence of this shows up fairly soon after she has drawn this conclusion.
She casts a suspicious eye when you are going out to hang out with your friends.
She believes something else.
Are you going to hang out with your friends, or someone else, maybe an ex?
Believing what you say is harder to swallow.
Voicing that you love her falls on disbelieving ears.
She thinks, “Well, if he loves me so much, why does he hide his past from me?”
“Doesn’t he trust me?”
“Can I trust him?”
It’s harder to win her trust back at this stage.
No matter what she hears from you, it’s challenging to trust anything that you say.
A planned business trip means you are detouring to see some girl on the side.
A message from a platonic female friend on social media means you are talking to this girl on the side.
She is paranoid with worry, leaving her to interpret anything mundane that you do as a sign of trouble.
Why burden your relationship with her by being so tight-lipped?
Provide pertinent information about your past relationships that are relevant and warranted, so that these seeds of doubt never develop.
Acting too late in sharing relevant information about your past relationships is a ticket to sending her down a mental rabbit hole she loses herself in, and salvaging the relationship at this juncture is much harder.